Many products that have historically been produced from natural materials or materials reinforced with steel are now being produced from fiber-reinforced plastics. For instance, golf club shafts, fishing poles, skis, snowboards, and a host of other products that were once made from natural wood or metal tubing, are now being produced from matrix resins reinforced with high-modulus fibers such as carbon, aramid, and the like. The high-modulus fibers used in these applications may be short chopped fibers dispersed in a matrix resin, continuous strands of filament impregnated with matrix resin, or fabrics that have been mandrel-wound, stitch-bonded, knitted, or woven into desired structural forms. These fiber-reinforced plastic structures are finding ever-increasing usage and acceptance in the marketplace as both replacements for conventional products and innovative new product forms.
There is an economic problem associated with the production of continuous fine filament high-modulus strands, in that they are relatively expensive to produce, especially in the form of fine filament yarns. A plant designed to manufacture continuous filament strands can produce either coarse strands or fine strands. A coarse strand set-up will produce more pounds of filament per day than a fine strand set-up, and consequently fine filament strands will cost more per pound to produce than coarse filament strands. When specific applications call for very fine high-modulus filament strands, the cost to produce them may become prohibitive, and alternative lower-modulus materials that are less costly to produce end up being used for such applications.
A partial solution to the economic problems associated with production of fine high-modulus strands is to convert relatively high-denier continuous filament tow strands into staple slivers that can be spun into fine textile spun yarns. For instance, in the case of carbon filaments, U.S. Pat. No. 4,825,635 to Gueval et al. describes a process wherein multifilament carbon yarns of 1500–20,000 denier are converted into staple fibers using a slow multi-step process involving “cracking by drawing and controlled breaking”, yielding fibers whose average length is 100 to 120 mm (3.9 to 4.7 inches). The fibers are then spun into yarn using standard spinning equipment, which would typically involve the sequence of breaker drawing, finisher drawing, roving, and spinning. Such a yarn is deficient in physical properties, in that Guevel notes that 30 percent of the original strength of the filament carbon yarn is lost in formation of this spun yarn.